Changes

|'''TLP621-4''' (×2)||"T8K TLP621-4 GB"||16-DIP||Quad transistor-output optocoupler, 5 kVrms isolation, CTR 100–600 %. Together they provide 8 isolated digital channels — sufficient for the AD7543's serial interface (SRI data, STB clock, LD load, CLR clear), master enable, fault status, plus the two AD654 frequency-out telemetry channels.||[https[://uk.farnellFile:TLP621 datasheet.com/toshiba/tlp621-4-gb/optocoupler-quad-5kv-transtr-o/dp/1225839 Farnell pagepdf|Datasheet]]

|'''TLP621''' (×1)||"T7K P621"||4-DIP||Single-channel version. Probably an additional status / interlock line, or a high-priority signal kept on its own isolation domain.||[https[://toshiba.semicon-storage.com/us/semiconductor/product/isolators-solid-state-relaysFile:TLP621 datasheet.html Toshiba familypdf|Datasheet]]